Jorryt Matthee
@jorryt.bsky.social
Extragalactic astrophysicist. Assistant Prof @ IST Austria - PI of ERC StG-2022 AGENTS. PhD Leiden 2018, Zwicky fellow @ ETH Zurich,2018-2023.
With toy models, we investigate how selection effects impact the observed MZR, and whether an intrinsically steep MZR may be masqueraded. The direction of this effect depends on whether the 3D correlation between stellar mass, star formation rate and metallicity known at z=0 evolves or not.
October 31, 2025 at 10:53 AM
With toy models, we investigate how selection effects impact the observed MZR, and whether an intrinsically steep MZR may be masqueraded. The direction of this effect depends on whether the 3D correlation between stellar mass, star formation rate and metallicity known at z=0 evolves or not.
However, our measurements (and thus the literature implied) do not match recent galaxy simulations, especially once we account for our known selection effects. This implies that the MZR is flatter than expected, suggestive of more rapid chemical enrichment in low-mass galaxies.
October 31, 2025 at 10:53 AM
However, our measurements (and thus the literature implied) do not match recent galaxy simulations, especially once we account for our known selection effects. This implies that the MZR is flatter than expected, suggestive of more rapid chemical enrichment in low-mass galaxies.
The mass-metallicity relation of our sample confirms that early galaxies have a lower oxygen abundance than galaxies in the local Universe, with values and a mass-dependence in broad agreement with recent measurements in the literature based on other surveys and instruments.
October 31, 2025 at 10:53 AM
The mass-metallicity relation of our sample confirms that early galaxies have a lower oxygen abundance than galaxies in the local Universe, with values and a mass-dependence in broad agreement with recent measurements in the literature based on other surveys and instruments.
We use these stacks to measure the direct Te-based gas-phase oxygen abundance in various stacks of galaxies, and we demonstrate that previously calibrated strong line calibrations between the [OIII]/Hb ratio and metallicity are also applicable to our sample.
October 31, 2025 at 10:53 AM
We use these stacks to measure the direct Te-based gas-phase oxygen abundance in various stacks of galaxies, and we demonstrate that previously calibrated strong line calibrations between the [OIII]/Hb ratio and metallicity are also applicable to our sample.
By combining deep NIRCam grism data from the EIGER, ALT and COLA1 surveys, we assembled a clean oxygen emission-line selected sample of nearly 1000 galaxies in the early Universe at z~6. In stacked spectra, we detect feature as faint as [OIII]4364.
October 31, 2025 at 10:53 AM
By combining deep NIRCam grism data from the EIGER, ALT and COLA1 surveys, we assembled a clean oxygen emission-line selected sample of nearly 1000 galaxies in the early Universe at z~6. In stacked spectra, we detect feature as faint as [OIII]4364.
2) a significant population of quenched galaxies at low masses and/or 3) an under-estimate in the dust attenuation from SED modeling at the massive end.
October 28, 2025 at 11:02 AM
2) a significant population of quenched galaxies at low masses and/or 3) an under-estimate in the dust attenuation from SED modeling at the massive end.
With boundary constraints from simulations ("the slope must be 1"), our data does prefer an increasing scatter towards low masses, which confirms the picture of bursty star formation in low mass galaxies.
October 28, 2025 at 11:02 AM
With boundary constraints from simulations ("the slope must be 1"), our data does prefer an increasing scatter towards low masses, which confirms the picture of bursty star formation in low mass galaxies.
We show that the flat slope is partly due to the flux-limited nature of our survey. Yet, even correcting for this with a Bayesian model, our data prefers a flatter slope, with a scatter that we cannot constrain on our data alone.
October 28, 2025 at 11:02 AM
We show that the flat slope is partly due to the flux-limited nature of our survey. Yet, even correcting for this with a Bayesian model, our data prefers a flatter slope, with a scatter that we cannot constrain on our data alone.
At face value, our data yields a relatively flat slope of the main sequence, which other work recently also reported, but which is at odds with virtually every galaxy simulation and with the relative constant low mass slope of the galaxy stellar mass function.
October 28, 2025 at 11:02 AM
At face value, our data yields a relatively flat slope of the main sequence, which other work recently also reported, but which is at odds with virtually every galaxy simulation and with the relative constant low mass slope of the galaxy stellar mass function.
Thanks to JWST grism spectroscopy behind a lensing cluster, we can now obtain large samples of uniformly selected galaxies at redshifts z~5, whose star formation rates we accurately estimate with the Halpha line, and characterize the main sequence across three orders of magnitude in mass.
October 28, 2025 at 11:02 AM
Thanks to JWST grism spectroscopy behind a lensing cluster, we can now obtain large samples of uniformly selected galaxies at redshifts z~5, whose star formation rates we accurately estimate with the Halpha line, and characterize the main sequence across three orders of magnitude in mass.
Delayed paper day! In work lead by my postdoc Claudia Di Cesare as part of the ALT survey, we provide a detailed census of the so-called star formation main sequence in the early Universe. arxiv.org/pdf/2510.19044
October 28, 2025 at 11:02 AM
Delayed paper day! In work lead by my postdoc Claudia Di Cesare as part of the ALT survey, we provide a detailed census of the so-called star formation main sequence in the early Universe. arxiv.org/pdf/2510.19044
Where are you all now?
October 15, 2025 at 5:46 PM
Where are you all now?
Puzzled by all the latest developments and observed features in LRDs? We tried to summarize the key features, our interpretation, alternatives and challenges in this table:
October 3, 2025 at 7:54 AM
Puzzled by all the latest developments and observed features in LRDs? We tried to summarize the key features, our interpretation, alternatives and challenges in this table:
What does this mean? This very luminous LRD likely resides in a very low mass galaxy. The BH mass is unlikely as high as the virial indicators suggest, because the broadening is not dynamical. What the BH mass is.. a wide range is still possible, and we should find new ways of figuring that out!
October 3, 2025 at 7:54 AM
What does this mean? This very luminous LRD likely resides in a very low mass galaxy. The BH mass is unlikely as high as the virial indicators suggest, because the broadening is not dynamical. What the BH mass is.. a wide range is still possible, and we should find new ways of figuring that out!
Despite most of the light being dominated by the "LRD" (which we think is an accreting SMBH highly covered by dense gas), there are some indications of host galaxy light, in particular the extremely narrow [OIII] emission and some (similarly) narrow Hgamma emission that pops up
October 3, 2025 at 7:54 AM
Despite most of the light being dominated by the "LRD" (which we think is an accreting SMBH highly covered by dense gas), there are some indications of host galaxy light, in particular the extremely narrow [OIII] emission and some (similarly) narrow Hgamma emission that pops up
Using Cloudy modeling, we can connect the various observed features: [FeII], scattering & collisionally dominated Balmer emission and the now well-known Balmer break of LRDs: a warm layer of dense gas (T~7000 K, ne~10^9 cm3) is responsible.
October 3, 2025 at 7:54 AM
Using Cloudy modeling, we can connect the various observed features: [FeII], scattering & collisionally dominated Balmer emission and the now well-known Balmer break of LRDs: a warm layer of dense gas (T~7000 K, ne~10^9 cm3) is responsible.
The most surprising observed feature is a forest of [FeII] emission lines -- these lines are commonly observed in quasars but they tend to be much broader. This is further evidence that the dense gas is not moving as rapidly as the line-widths of the Balmer lines suggest.
October 3, 2025 at 7:54 AM
The most surprising observed feature is a forest of [FeII] emission lines -- these lines are commonly observed in quasars but they tend to be much broader. This is further evidence that the dense gas is not moving as rapidly as the line-widths of the Balmer lines suggest.
With our new deep JWST NIRspec IFU Prism+G395H data, we can characterize the Balmer lines in unprecedented detail; We confirm the absorption seen in grism data, show it's also present in other transitions, and we argue the line-profiles are best explained by exponential wings with P Cygni cores.
October 3, 2025 at 7:54 AM
With our new deep JWST NIRspec IFU Prism+G395H data, we can characterize the Balmer lines in unprecedented detail; We confirm the absorption seen in grism data, show it's also present in other transitions, and we argue the line-profiles are best explained by exponential wings with P Cygni cores.
Object of interest: FRESCO-GN-9771, the most luminous LRD from my discovery paper (arxiv.org/abs/2306.05448). This object shows such luminous Halpha emission that I initially thought it must have been a very nearby object when I spotted it in the FRESCO data back in 2023.. Yet it's at z~5.5.
October 3, 2025 at 7:54 AM
Object of interest: FRESCO-GN-9771, the most luminous LRD from my discovery paper (arxiv.org/abs/2306.05448). This object shows such luminous Halpha emission that I initially thought it must have been a very nearby object when I spotted it in the FRESCO data back in 2023.. Yet it's at z~5.5.
Delayed paper day!
arxiv.org/abs/2510.00103
Led by Alberto Torralba, who is a postdoc in my group, we present the highest quality spectrum of a "Little Red Dot" yet known. This unveils new insights in the warm, dense layer of gas that is key to explain the most unusual spectral features of the LRDs!
arxiv.org/abs/2510.00103
Led by Alberto Torralba, who is a postdoc in my group, we present the highest quality spectrum of a "Little Red Dot" yet known. This unveils new insights in the warm, dense layer of gas that is key to explain the most unusual spectral features of the LRDs!
October 3, 2025 at 7:54 AM
Delayed paper day!
arxiv.org/abs/2510.00103
Led by Alberto Torralba, who is a postdoc in my group, we present the highest quality spectrum of a "Little Red Dot" yet known. This unveils new insights in the warm, dense layer of gas that is key to explain the most unusual spectral features of the LRDs!
arxiv.org/abs/2510.00103
Led by Alberto Torralba, who is a postdoc in my group, we present the highest quality spectrum of a "Little Red Dot" yet known. This unveils new insights in the warm, dense layer of gas that is key to explain the most unusual spectral features of the LRDs!
We make these and various other new calibrations available in the paper, discuss what to do if you worry about attenuation due to dust and how biased various measurements of galaxy populations otherwise are. 6/..
September 9, 2025 at 4:05 PM
We make these and various other new calibrations available in the paper, discuss what to do if you worry about attenuation due to dust and how biased various measurements of galaxy populations otherwise are. 6/..
However, fortunately, the Halpha equivalent width -- a measurement readily available for many galaxies -- correlates with both of these quantities and can be used to derive more accurate and bias-free measurements of the rates at which young galaxies form new stars .. 5/
September 9, 2025 at 4:05 PM
However, fortunately, the Halpha equivalent width -- a measurement readily available for many galaxies -- correlates with both of these quantities and can be used to derive more accurate and bias-free measurements of the rates at which young galaxies form new stars .. 5/
Indeed, using the SPHINX20 simulation we show that the SFR-Bias (how wrong is your star formation rate if you use the standard calibration) correlates both with burst age and metallicity. Unfortunately, it is not very easy to simply measure these properties and use those to derive corrections... 4/.
September 9, 2025 at 4:05 PM
Indeed, using the SPHINX20 simulation we show that the SFR-Bias (how wrong is your star formation rate if you use the standard calibration) correlates both with burst age and metallicity. Unfortunately, it is not very easy to simply measure these properties and use those to derive corrections... 4/.
The Halpha emission line has long been considered the "golden" indicator of the star formation rate of galaxies. However, various assumptions behind the standard calibrations are no longer applicable to galaxies in the early Universe such as those observed by the JWST, causing significant bias 2/..
September 9, 2025 at 4:05 PM
The Halpha emission line has long been considered the "golden" indicator of the star formation rate of galaxies. However, various assumptions behind the standard calibrations are no longer applicable to galaxies in the early Universe such as those observed by the JWST, causing significant bias 2/..
May 19, 2025 at 6:42 AM